This project is oriented toward determination of mechanisms of the control of respiration. The specific areas of investigation: (1) The role of peripheral arterial chemoreceptors in regulation of breathing in acclimatization to chronic hypoxia and during exercise, (2) The mechanism of recovery of peripheral chemoreceptor function following denervation, and (3) The verification of and mechanisms of "cardiodynamic hyperpnea", i.e., the increased breathing during exercise which is related to increased pulmonary blood flow. We are using awake, trained goats and ponies to investigate these areas. Some of these animals will be subjected to surgical denervation of the peripheral chemoreceptors in the course of the experiments. Measurements consist of pulmonary expired ventilation, respiratory frequency, tidal volumes, metabolic rate, heart rate, blood pressure, cardiac output, blood gases and acid-base status and ventilatory responses to acute and long term hypoxia and to transient tests to determine function of peripheral chemoreceptors.